Integrated geophysical and geological characterization of oil sand in Eastern Dahomey Basin Southwestern, Nigeria

Abstract

An integrated geophysical and sedimentological study was conducted to characterize oil sand deposits in the Dahomey Basin. Six traverses were surveyed using Electrical Resistivity Tomography (ERT) and Seismic Refraction Tomography (SRT), complemented by grain-size and heavy mineral analyses of collected samples. ERT revealed high-resistivity zones (≈2500– > 250,000 Ωm), interpreted as bitumen-saturated sands, while SRT showed intermediate P-wave velocities (≈1900–2300 m/s), confirming the mechanical properties of the oil sand layer. Thickness discrepancies between ERT (≈5–30 m) and SRT (≈12–34 m) are attributed to method-specific sensitivities to electrical versus elastic properties. Sedimentological analyses indicate moderately sorted medium sands (mean = 1.07–1.38 φ) with ZTR indices of 57–67%, and heavy minerals dominated by zircon, rutile, and tourmaline, suggesting a proximal felsic–metamorphic source, moderate transport, and deposition in a fluvio-marine transitional environment. The shallow depth (0–3 m), significant thickness, lateral continuity, and favorable granulometric and mineralogical properties suggest potential economic significance. The study demonstrates that integrating geophysical imaging with sedimentological characterization provides robust constraints on subsurface oil sand distribution and reservoir quality, thereby offering valuable guidance for resource evaluation and extraction planning.